Forgive me if I repeat anything, but I haven't been on this page for months (no-one will remember me probably), but if part four is a possibility, then is it not fairly straightforward the most obvious way to work it would be Garcia as an older vincent, de niro to play an older vito circa wars with the irish, pacino to play the reluctant consigliere post marys death, and a newbie to play the young sonny in the vito days. I know the lack of brando is off putting (he is the godfather), but i can see no other way of playing it. The flash backs of GF2 would be an appropriate structure for development. Again apologies if this is a fairly common thought but i had to post my thoughts.